The perception of breathlessness in asthma

We studied the perception of breathlessness as a function of air flow obstruction in 45 asthmatic subjects using a category scaling technique. Air flow obstruction and breathlessness were induced by inhalations of histamine acid phosphate in twofold-increasing concentrations from 0.03 to 16 mg/ml. The FEV1 was measured after each inhalation of histamine, and the subject was asked to rate his symptoms of breathlessness. The results showed that breathlessness increased as the FEV1 decreased but, despite a close linear relationship in all subjects (mean r = 0.88 +/- 0.15 SD), there was a considerable variation in the severity of breathlessness for any particular degree of air flow obstruction (mean intercept, 0.50 +/- 0.89 SD). However, the increase in sensory magnitude with increasing air flow obstruction did not show the same degree of variability (mean slope, 0.13 +/- 0.06 SD). The variability in breathlessness in asthmatic patients is likely to have many components. Two of these components were identified. First, we found that there was less respiratory distress in those subjects in whom air flow obstruction was present at the onset of the study. However, the presence of air flow obstruction at this time does not result in a reduction in sensation for further increases in air flow obstruction as might be expected from discrimination studies. Second, there was a significant relationship (p less than 0.01) between bronchial responsiveness and the magnitude of respiratory distress. Those subjects highly responsive to histamine experienced less respiratory distress than the less responsive subjects.

Human leukocyte elastase, cathepsin G, and lactoferrin: family of neutrophil granule glycoproteins that bind to an alveolar macrophage receptor

Interactions between polymorphonuclear neutrophils and mononuclear phagocytes are potentially of great importance in a variety of inflammatory processes. As part of a continuing effort to elucidate the physiologic importance of human alveolar macrophage receptor-mediated binding of neutrophil (leukocyte) elastase, I have studied the binding of leukocyte elastase and two other neutrophil granule glycoproteins, cathepsin G and lactoferrin, to human alveolar macrophages. Saturable binding of all three ligands at 0 degrees C was observed, with equilibrium dissociation constants of 4.0 x 10(-7), 2.0 x 10(-7), and 1.7 x 10(-6) M, respectively. All bound to a similar number (54-73 x 10(6)) of sites per cell. Binding of all three ligands was inhibited by the polysaccharide fucoidin, and extensive cross-inhibition of their binding to macrophages was observed. The results indicate that alveolar macrophages possess a relatively low-affinity, high-volume receptor for a family of neutrophil granule glycoproteins, which would be ideally suited for clearing released neutrophil granule contents from the extracellular space in inflamed tissues.

Proteolysis by neutrophils. Relative importance of cell-substrate contact and oxidative inactivation of proteinase inhibitors in vitro

Polymorphonuclear leukocytes have been implicated in connective tissue injury in a variety of disease processes. To gain insight into mechanisms by which neutrophils might degrade connective tissue macromolecules in the presence of proteinase inhibitors, we have used a model system that allows neutrophils to be held in vitro under physiologic conditions in close proximity to a very proteinase-sensitive substrate, (125)I-labeled fibronectin. We have found: (a) neutrophils spread rapidly on the fibronectin substrate; (b) fibronectin proteolysis by neutrophils is largely attributable to released elastase, and is linearly related to cell number over the range of 2,000 to 30,000 cells per assay; (c) oxidants released from neutrophils stimulated by opsonized zymosan or phorbol myristate acetate do not protect released elastase from inhibition by alpha(1)-proteinase inhibitor or alpha(2)-macroglobulin; (d) neutrophil myeloperoxidase and enzymatically generated superoxide anion render alpha(1)-proteinase inhibitor ineffective against fibronectin proteolysis when neutrophils are added 30 min later; and (e) alpha(1)-proteinase inhibitor and alpha(2)-macroglobulin incompletely inhibit fibronectin proteolysis by neutrophils (79.8+/-6.3 and 73.5+/-12.0%, respectively.) The data suggested that proteolysis due to neutrophils that are in contact with susceptible macromolecules may occur due to partial exclusion of inhibitors from the cell-substrate interface. Although confirming that alpha(1)-proteinase inhibitor is ineffective against neutrophil-derived proteolysis after exposure to oxidants, these studies did not support the hypothesis that oxidants released from stimulated neutrophils enhance activity of proteinases they release in the presence of alpha(1)-proteinase inhibitor. We anticipate that further studies with this test system will be helpful in defining conditions that modulate inflammatory connective tissue injury in diseases such as pulmonary emphysema and rheumatoid arthritis.

Effect of ventilatory drive on the perceived magnitude of added loads to breathing

Using open-magnitude scaling we studied the importance of ventilatory drive on the perceived magnitude of respiratory loads by applying a range of externally added resistances (2.1-77.1 cmH2O X l-1 X s) to normal subjects at rest and at three increasing levels of ventilatory drive induced by exercise, CO2-stimulated breathing, and hypoxia. Under all conditions studied the perceived magnitude of the added loads increased with the magnitude of the resistive load and as the underlying level of ventilatory drive increased. When the results were expressed in terms of peak inspiratory pressure, the perceived magnitude was related to the magnitude of the peak inspiratory pressure by a power function (mean r = 0.97). These results suggest that the perceived magnitude of added resistive loads increased with increasing ventilatory drive, in such a manner that the increase in sensory magnitude is proportional to the increase in the inspiratory muscle force developed and suggests that something dependent on this force mediates the sensation.

Detection latency of added loads to breathing

1. Detection latency of a range of added elastic (0.95-4.50 kPa/l) and resistive (0.73-3.29 kPa l-1 s) loads to breathing were measured in five normal subjects. Detection latency was defined as the time from the onset of the breath to detection of the load. 2. Detection latency followed a curvilinear relationship when plotted as a function of the magnitude of the added loads. A similar relationship was found with both elastic and resistive loads although detection latencies to added elastances were longer than for added resistances. 3. When the added load was expressed in terms of comparable magnitude (peak inspiratory pressure) detection latencies for added elastances were found to be consistently longer than for added resistive loads. 4. These studies show that the detection latency to added inspiratory loads follows a reciprocal relationship, that detection latencies for elastic and resistive loads are clearly different and suggest that these loads are detected during the respiratory cycle at a time when the mechanical information regarding muscular pressure is greatest.

Lung volume, closing volume, and gas exchange

The effect of a voluntary reduction in lung volume on arterial O2 saturation (SaO2) was studied in 10 normal subjects aged 19-63 yr. SaO2 was measured by ear oximetry first during tidal breathing at functional residual capacity, and then during tidal breathing at 380 ml above residual volume. Tidal volume and breathing frequency were kept constant, and end-tidal CO2 partial pressure remained stable or fell in 9 out of 10 subjects. When lung volume was reduced, SaO2 fell by a mean of 1.5% (range 0-3%). Closing volume (CV) was measured by the N2-washout method (mean 0.89 liter, range 0.41-1.44). There was a close correlation between CV and the fall in SaO2 (r = 0.867, P = 0.001). Arterial and mixed venous CO2 were measured in one subject; the results indicated some fall in cardiac output following the lung volume change, but this accounted for less than half of the fall in SaO2. The relationship between CV and the lung volume at which tidal breathing occurs is an important determinant of pulmonary gas exchange through its effect on the matching of ventilation to perfusion.

Some physical signs in patients with chronic airflow obstruction

Forty subjects with chronic airflow obstruction were examined independently by 2 observers, and their assessment of several physical signs was recorded. Spirometry and lung volumes were measured. Most of the signs studied correlated closely with the degree of airflow obstruction as assessed by the forced expiratory volume in one second. Certain signs also correlated closely with the degree of hyperinflation, the duration of symptoms, or the age of the subject. The agreement between observes in this study was good. Although all the signs are related in one way or another to the severity of airflow obstruction, some are due to large variations in intrathoracic pressure, some to hyperinflation and some, possibly, to changes in the shape of the chest and the action of the respiratory muscles. Hence, we suggest that these signs should not be regarded as inferior to tests of pulmonary function; physical examination and spirometry should be complementary.

Effect of breathing patterns on the perceived magnitude of added loads to breathing

We have studied the perceived magnitude (psi) of a range of externally added resistive (delta R) and elastic (delta E) loads to breathing while varying the flow rate, tidal volume, and inspiratory duration. The sensory magnitude of an added resistive load increased with both the inspiratory flow rate (P less than 0.001) and the magnitude of the added resistance (P less than 0.01). Similarly, the perceived magnitude of an added elastic load increased with both the tidal volume (P less than 0.001) and the magnitude of the added elastance (P less than 0.01). When inspiratory duration was not controlled, a single relationship was found to hold for both types of load when analyzed as a function of inspiratory airway pressure (P): psi = K . P1.15 (r = 0.94 for delta R); psi = K . p1.10 (r = 0.98 for delta E). When inspiratory duration was controlled, the perceived magnitude of both resistive and elastic loads also increased as the inspiratory duration increased (P less than 0.05). Again, the sensory magnitude was closely related to the airway pressure; but for any given airway pressure the perceptual magnitude also increased as inspiratory duration increased: psi = K . t0.6 (for delta R); psi = K . t0.52 (for delta E). When resistive, elastic, and mixed resistive and elastic loads were presented while keeping inspiratory duration constant, the sensory magnitude was directly related to the airway pressure (r = 0.99) and there was no discernible difference between the types of load. The results suggest that the perceived magnitude of added loads to breathing is directly related to the inspiratory muscle force and its duration (psi = K . P1.3 . t0.56) and indirectly to the added load.

Elastase of U-937 monocytelike cells. Comparisons with elastases derived from human monocytes and neutrophils and murine macrophagelike cells

As an approach to facilitating the understanding of proteinases associated with monocytes we have studied U-937 monocytelike cells. Elastase activity was identified in U-937 cell extracts and compared to monocyte elastase activity, neutrophil elastase, and the elastase activity from a continuous line of murine macrophagelike cells (P388D1). Serine proteinase activity which solubilized (14)C-labeled elastin accounted for >90% of the neutral proteinase activity of both U-937 cells and monocyte extracts. U-937 cell and monocyte elastase activities were similar catalytically, resembling neutrophil elastase. U-937 cells and monocytes showed other similarities: (a) both had activities reacting with [(3)H]diisopropylfluorophosphate that migrated in sodium dodecyl sulfate (SDS) polyacrylamide gels at approximately 30,000 and 60,000 daltons and (b) both contained material that cross-reacted with antiserum raised to neutrophil elastase. Preliminary characterization of U-937 cell elastase activity by affinity chromatography and ion-exchange chromatography suggested the presence of at least two distinct elastases. Minimal elastase activity was found in U-937 cell-conditioned medium, indicating that the activity is not spontaneously released by the cells. In contrast to the elastase activity associated with U-937 cells and monocytes, the elastase activity associated with P388D1 cells was a metalloproteinase and was found principally in the culture medium. These results indicate (a) U-937 cells will be useful for further investigation of proteinases associated with normal monocytes; (b) monocytes and U-937 cells contain material with catalytic and immunologic similarities to neutrophil elastase; (c) monocyte elastase activity differs from elastase activity secreted by murine macrophages and murine macrophagelike cells of the P388D1 line.

Effect of digoxin on right ventricular function in severe chronic airflow obstruction. A controlled clinical trial

The effect of digoxin on the right and left ventricular ejection fractions in 15 patients with pulmonary heart disease caused by severe chronic airflow obstruction was studied in a double-blind, randomized, placebo-controlled trial. All patients were ambulatory and had clinical features of right but not left ventricular dysfunction. Equilibrium radionuclide angiography showed reduced right ventricular ejection fraction in all patients and reduced left ventricular ejection fraction in four. After 8 weeks of digoxin treatment, the abnormal left ventricular ejection fractions were normal; right ventricular ejection fractions increased only in those patients who had had abnormal left ventricular ejection fractions. We conclude that in patients with pulmonary heart disease, the right ventricular ejection fraction is abnormal and improves with digoxin treatment only when the left ventricular ejection fraction also is initially abnormal.

Cell injury and repair

Occupational lung disease results from a remarkably complex interaction of the inhaled material with the lung parenchyma and the worker's immune and inflammatory mechanism, (Fig 1). The past decade has seen a marked increase in our understanding of individual events involved in the pathogenesis of occupational lung disease, and has seen increased appreciation of the prominent role of lung inflammation in the production of lung disease following inhalation of a potentially injurious agent. Further work with isolated cells and tissue in culture and with experimental animal models will be required to assess the contribution of individual pathogenetic events to the total disease picture, and to better understand the ability of the lung parenchyma to repair itself following injury.

The quantification of respiratory sensations by normal subjects

The technique of open magnitude scaling was used in normal subjects to define the exponent (n) of Stevens; psychophysical power law for four respiratory variables: tidal volume (VT), inspiratory flow (V), ventilation (Ve), and frequency (f). Stevens' psychophysical law states that the perceived magnitude (psi) of a stimulus is related to the physical magnitude (phi) by a constant (k) and an exponent (n): psi = kappaphin. The mean value of n was for VT 1.14 plus or minus 0.08 (SEM), V 1.13 plus or minus 0.15, for Ve 1.28 plus or minus 0.11 and for f 1.04 plus or minus 0.15. These results show that these respiratory variables are judged with an expanded sensory scale. The similarity of exponents for VT and V leaves open the possibility tht both are sensed by the same neurophysiological mechanism. Further experiments on VT showed that both passive ventilation and chest vibration impaired the ability of subjects to accurately judge tidal volumes. Our results indicate that the sensation of volume is mediated by afferent information generated by receptors affected by respiratory muscle concentration.

The contribution of upper airway and inspiratory muscle mechanisms to the detection of pressure changes at the mouth in normal subjects

1. With standard psychophysical techniques the ability of normal subjects to detect negative pressures applied at the mouth was estimated. 2. The ability to detect changes in pressure when confined to the upper airway by closure of the glottis was less than when the pressures were transmitted below the glottis and were actively overcome by inspiratory muscle contraction. 3. The ability to detect changes in pressure with the glottis open was also impaired by passive ventilation and vibration of the chest. 4. Our results imply that the most sensitive mechanism for the detection of negative pressures applied at the mouth involves afferent information from active inspiratory muscle contraction.

The effect of respiratory muscle fatigue on respiratory sensations

1. Eight subjects maintained maximal inspiratory pressure as long as possible. The subjects accurately judged the pressure developed, but considered that the sense of effort or motor command increased progressively during the contraction as fatigue developed. 2. A reference inspiratory load was overestimated after maximal inspiratory contractions. 3. These findings are consistent with the hypothesis that awareness of the motor command or effort contributes to the estimation of respiratory loads.

Magnitude scaling of externally added loads to breathing

Externally added resistive and elastic loads to breathing elicit a sensation the psychological magnitude of which was described by a power function: psi = k theta n. The perceived magnitude (psi) was related to the physical magnitude (theta) by the exponential term (n). The exponent described the increase in sensation for an increase in load. In normal subjects, the mean exponent for added resistive loads was 0.80 +/- 0.35 SD, and for elastic loads was 0.99 +/- 0.45. Intrasubject variability (mean coefficient of variation = 7%) was much less than intersubject variability (coefficient of variation = 230%). The exponents for elastance and resistance were highly correlated (r = 0.92). In these studies, the subjects freely adopted their tidal volume and flow rate. During the addition of resistive loads, the subjects tended to reduce their flow rate, especially at the highest loads, and during the elastic loads, they tended to reduce their tidal volume. Fixing tidal volume during the addition of elastic loads and flow rates during the addition of resistive loads caused an increase in exponent. This finding implied that the tidal volume and flow rate, or factors related to them such as muscular effort, are important attributes of the sensation elicited by loaded breathing.

Effect of timing, flow, lung volume, and threshold pressures on resistive load detection

The acuity of resistive load detection (RLD) has been tested by comparing threshold detection (delta R50) under control conditions with that obtained when loads were applied at different times in inspiration, with different inspiratory flows, at different lung volumes, and with different background loads. For loads applied suddenly during established inspiratory flow, the mean delta R50 was 0.94 +/- 0.04 (+/- SEE) cmH2O . 1(-1) . s compared with 0.42 +/- 0.13 cmH2O . 1(-1) . s (P < 0.01) for loads applied before inspiration, suggesting that information generated early in the breath is important and the RLD is not subserved by a simple peripheral proprioceptive mechanism. Rapid voluntary inspiration through nonlinear resistances did not improve RLD (mean delta R50 0.86 cmH2O . 1(-1) . s compared with a control of 0.56 cmH2O . 1(-1) . s; P < 0.05) despite the much greater pressures and resistances at high flow rates, further suggesting that detection of a resistive load occurs early in inspiration. Alteration of the background load by breathing at increased lung volume (1 liter above FRC) or by breathing against a standing pressure of 1 or 3 cmH2O (i.e., pressure independent of volume or flow) did not significantly reduce RLD. This suggests that the change in pressure due to the added load, expressed as a fraction of the total driving pressure, cannot subserve RLD. Our results suggest that external resistive load detection is subserved by the relation between pressure and flow over the early part of inspiration.

Changes in the perception of inspiratory resistive loads during partial curarization

1. The ability of normal subjects to estimate the magnitude of resistive loads and to detect resistive loads was determined using standard psychophysical techniques. The experiments were repeated during maintained partial neuromuscular blockade with D-tubocurarine. 2. During curarization the ability to detect the presence of a small inspiratory resistive load was not significantly impaired. This finding is consistent with the view that changes in the usual breath-by-breath relation between pressure and flow mediate detection. 3. The size of resistive loads was over-estimated during partial curarization. Subjects thus placed more reliance on sensing the increased motor command required during curarization than on alternative peripheral signals related to pressure, flow or resistance. 4. The exponent for the power function relating the perceived magnitude of a resistive load to its actual size (Stevens, 1957) was reduced during partial neuromuscular blockade. 5. These results suggest that detection of resistive loads depends upon sensing apparent information arising from an unexpected pressure-flow disturbance but that estimation of the size of an added load depends, in part, on sensing the outgoing motor command.

Resistive load detection during passive ventilation

By using standard psychophysical techniques resistive load detection was estimated in five normal subjects during spontaneous breathing and during passive ventilation in a Drinker respirator. 2. During assisted ventilation a gross deterioration in resistive load detection occurred. 3. The findings imply that active respiratory muscle contraction plays an essential role in the detection of added resistive loads.

Importance of airway closure in limiting maximal expiration in normal man

To elucidate the importance of airway closure in limiting maximum expiration, two complementary plethysmographic techniques have been used to estimate the volume of and pressure within the trapped thoracic gas. Three young (19-23 yr) and three older (43-66 yr) subjects were studied. The first study defined the curve of possible pressure-volume relationships for the trapped gas; the second study attempted to estimate the volume of trapped gas. In the first study the subject in a Mead plethysmograph expired through a pneumotachograph and back into the box. A reduction in box volume greater than that caused by drying and cooling of expired gas implies gas compression due mainly to airway closure. In the second study a known volume of air was withdrawn from the mouth at full expiration and changes in box volume and mouth pressure were recorded. The apparent volume in pressure communication with the mouth (Vpc) was calculated using Boyle's law. In the young subjects we did not detect thoracic gas compression although there was evidence of trapped gas (RV-Vpc greater than 0). In the older subjects there was a larger volume of trapped gas that was compressed to pressures of more than 22 cmH2O. Airway closure appears to limit maximal expiration in older subjects.

The effect of increased ventilation on resistive load discrimination

The ability of normal subjects to detect the addition of external resistive loads was determined both at rest and when ventilation was increased to more than 30 L/min by CO2 administration or exercise. Tidal volume, flow, and mouth and transpulmonary pressures were recorded during resistive load discrimination using standard psychophysical techniques. The mean resistance detection threshold was 0.40 +/- 0.06 cm H2O/L/s at rest, 0.36 cm H2O/L/s during administration of CO2, and 0.44 cm H2O/L/s with exercise. The Weber fraction was 0.28 +/- 0.04 at rest, 0.29 +/- 0.08 with CO2, and 0.34 +/- 0.04 with exercise. The lack of change in the ability to detect resistive loads when ventilation was increased was surprising because changes in both pressure and flow were tripled. The findings were supportive of the hypothesis that resistance or something like it is perceived, rather than change in flow or pressure.

The concept of disease

The connotations of the term "a disease" were investigated by studying the ways in which both medical and non-medical people used the word. A list of common diagnostic terms was read slowly to groups of non-medical academic staff of a university, secondary-school students, medical academics, and family practitioners, who then indicated whether they thought each word referred to disease.All groups rated illnesses due to infections as diseases, but the doctors, and particularly the general practitioners, were more generous in accepting as diseases the terms for non-infectious conditions. Apart from the nature of the cause, the most influential factor in determining whether or not an illness was considered to be a disease was the importance of the doctor in diagnosis and treatment.These findings provide further evidence that there is ambiguity about the meaning of the term disease. To the layman a disease seems to be a living agency that causes illness. Doctors have obviously accepted more heterogeneous defining characteristics but remain reluctant to adopt unequivocally nominalist ways of thought. The position is not unlike that in the physical sciences, in which there is a good precedent for distinguishing between the formal scientific and the everyday uses of terms such as "force" and "power."